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Indeterminate orbital masses: restricted diffusion at MR imaging with echo-planar diffusion-weighted imaging predicts
Ali R Sepahdari1, Vinay K Aakalu, Pete Setabutr
1Department of Radiology, Massachusetts General Hospital, 55 Fruit St, Gray 273A, Boston, MA 02114, USA. andrea.klauser@i-med.ac.at
Purpose:
To determine whether magnetic resonance (MR) imaging with diffusion-weighted (DW) imaging can help discriminate between radiologically indeterminate benign and malignant orbital masses and to identify optimal apparent diffusion coefficient (ADC) thresholds for such discrimination.
Materials And Methods:
Informed consent was waived for this HIPAA-compliant institutional review board-approved retrospective study. Forty-seven orbital masses imaged with echo-planar DW imaging were identified in 47 patients (25 female patients, 22 male patients; average age, 35 years). A fellowship-trained orbital surgeon determined reference-standard diagnoses on the basis of chart review, and a neuroradiology fellow and senior neuroradiologist who were blinded to the diagnoses selected a region of interest for each lesion by consensus. ADC was calculated from signal intensity on DW images obtained with b = 1000 and b = 0 sec/mm(2). Lesion ADC was also compared with that of normal-appearing white matter (ADC ratio). The Student t test was used to compare groups. Receiver operating characteristic analysis was performed. Intraobserver agreement was assessed with a repeat data collection.
Results:
Malignant lesions had lower ADCs than benign lesions, irrespective of patient age (P < .02) and in adults specifically (P < .05). Lymphomas had lower ADCs than pseudotumors (P < .001). An ADC of less than 1.0 x 10(-3) mm(2)/sec and an ADC ratio of less than 1.2 were optimal for predicting malignancy (sensitivity, 63% for both; specificity, 84% and 90%, respectively; and accuracy, 77% and 81%, respectively). Lymphoma was differentiated from pseudotumor with 100% accuracy (in 16 of 16 cases) by using these values. Infiltrative lesions that were hypointense on T2-weighted images were better characterized with DW imaging than lesions that were hyperintense or well defined.
Conclusion:
Echo-planar DW MR imaging can help characterize indeterminate orbital masses.
Insights
Diffusion-weighted magnetic resonance (MR) imaging helps differentiate benign and malignant orbital masses. Optimal apparent diffusion coefficient (ADC) thresholds aid in distinguishing between these lesions, improving diagnostic accuracy.
Area of Science:
- Radiology
- Oncology
- Ophthalmology
Background:
- Orbital masses present a diagnostic challenge, often requiring differentiation between benign and malignant conditions.
- Magnetic resonance (MR) imaging, particularly diffusion-weighted (DW) imaging, offers potential for improved characterization of these lesions.
Purpose of the Study:
- To evaluate the utility of DW MR imaging in discriminating between indeterminate benign and malignant orbital masses.
- To establish optimal apparent diffusion coefficient (ADC) thresholds for differentiating these lesions.
Main Methods:
- Retrospective analysis of 47 orbital masses in 47 patients using echo-planar DW MR imaging.
- Calculation of ADC values for each lesion and comparison with normal white matter (ADC ratio).
- Receiver operating characteristic analysis to determine optimal ADC thresholds for malignancy prediction.
Main Results:
- Malignant orbital masses demonstrated significantly lower ADC values compared to benign lesions.
- Optimal ADC thresholds of < 1.0 x 10(-3) mm(2)/sec and an ADC ratio of < 1.2 predicted malignancy with high specificity.
- DW imaging accurately differentiated lymphoma from pseudotumor (100% accuracy).
Conclusions:
- Echo-planar DW MR imaging is a valuable tool for characterizing indeterminate orbital masses.
- Established ADC thresholds can aid in distinguishing benign from malignant orbital lesions, including lymphoma and pseudotumor.
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